ANS:B - Vacuum residue

The most ideal feedstock for the 'coking' process used for the manufacture of petroleum coke is vacuum residue.

Explanation:

• Coking Process: This is a thermal cracking process used to convert heavy residual oils into lighter products and petroleum coke. The process operates at high temperatures to break down large hydrocarbon molecules.
• Vacuum Residue: This is the heavy residue left after vacuum distillation of crude oil. It contains large, complex hydrocarbon molecules that are ideal for coking.

Characteristics of Ideal Feedstock:

• High Molecular Weight: Vacuum residue consists of large molecules that break down under coking conditions to form lighter hydrocarbons and solid coke.
• High Carbon Content: This residue has a high carbon-to-hydrogen ratio, which is essential for producing high-quality petroleum coke.
• Low Value as Fuel: Vacuum residue has limited use as a fuel due to its high viscosity and low volatility, making it more suitable for conversion into valuable products like petroleum coke.

Unsuitable Feedstocks:

• Naphtha: This is a light, low-boiling fraction used primarily as a feedstock for petrochemical processes or as a blending component in gasoline. It lacks the high molecular weight needed for effective coking.
• Light Gas Oil: This is a distillate fraction that is typically used as diesel or heating oil. It is not heavy enough for the coking process.
• Diesel: This is another distillate product, primarily used as a fuel for diesel engines. Like light gas oil, it is not suitable for coking due to its lower molecular weight and boiling range.